A composite dipole antenna (CDA) structure forming an element of a larger array element, described in U.S. Pat. No. 6,999,041, (filed Feb. 16, 2004, issued Feb. 14, 2006, which is incorporated herein by reference in its entirety) contains a string of alternating resonant circuits. The function of the CDA array element is to receive radiation signals at two frequencies and reradiate a single signal at the difference frequency. This may be accomplished if the antenna incorporates one or more nonlinear device elements to achieve the conversion. One of the two circuit types is primarily a dipole antenna, and the second is primarily an impedance matching element between adjacent dipole antenna circuits. The second circuit type may contain, in addition to impedance matching components, a nonlinear device for enabling the frequency conversion. The quality (Q) value of these resonant circuits is an important characteristic that determines (among other parameters) the conversion efficiency of the CDA structure. The Q values of the resonant circuits are dependent on the various losses that are associated with them. Both circuit types may have conduction, dielectric and radiation losses. For various applications the CDA structure may be illuminated with electromagnetic beams of at least two frequencies f1 and f2 (where f1−f2=Δf, the difference frequency). In this case, both beams and also the difference frequency need to interact with both circuits of the CDA structure.
Where f1 and f2 are widely separated (in order to achieve a large value for Δf, i.e., cases where, for example, Δf>1% of f1,2) it may be necessary to lower the Q of both circuit types in order to facilitate an interaction between the fields and circuits, thus introducing losses that are undesirable from the point of view of conversion efficiency. In many cases it is required to design a CDA that operates with large Δf values (e.g., Δf>10% of f1,2, where f1,2˜(f1+f2)/2). Until now, broad band frequency generation, particularly in the millimeter and submillimeter wavelength terahetz frequency ranges have not been effectively achieved. As a result, there is a need to design CDA structures having both broad bandwidth capability and low losses.